Social Networks - Lecture 17

What is an ego network?

A network focused on one individual (the “ego”) and their direct connections.

How is an ego network different from a sociocentric network?

ego = just one person and their ties
sociocentric = all people and all ties in a defined population

What does the E-I Index measure in ego networks?

balance between external (out-group) and internal (in-group) ties.

What is a two-mode network (also called an affiliation matrix)?

A network with two types of nodes, and ties only occur between types (not within).

Example of a two-mode network?

people and events, authors and publication, students and clubs

What is a one-mode projection?

A simplified version of a two-mode network where nodes of the same type are connected based on shared ties to the other type​

What does a two-mode network give us when converted?

A weighted adjacency matrix showing how many shared affiliations each pair of nodes has.

Why do we use hypothesis testing in network analysis?

To test if an observed pattern (e.g., density, centrality) is statistically significant or random.

What is a permutation test and what is its goal?

A test that shuffles node attributes to see if the observed pattern is more extreme than what we’d expect by chance. The goal is to ask: “If people were randomly placed, would we still see this level of association?”

What is a CUG test?

Compares the observed network to random graphs with the same size and density. Helps determine whether a network’s characteristics (e.g., density) are unusual or expected based on random structure.